In recent years, a shift toward renewable energy, and electric power saving in electrical and electronic devices are progressing. Research and development in electric power saving are conducted continuously because of the fact that much of the energy resources of the nation's electric power depends on imports.
In information infrastructure, such as data centers, and the like, which supports information and communication technology (ICT), with the amount of data traffic that increases year by year, power supply is on the rise. Accordingly, electric power saving is promoted. For example, in systems that are used in data centers, and the like, optical communication systems using a phase-modulated optical signal generated by selecting one of a plurality of optical signals having different phases and time multiplexing, or the like are known. As related art, for example, Japanese Laid-open Patent Publication No. 2006-345416, and Japanese Laid-open Patent Publication No. 8-46570 are disclosed.
For electric power saving in an optical communication system, and the like, a method change in optical communication, or the like is considered. However, a method change is carried out after data communication in a system is stopped once so that the method change has a high risk. For this reason, electric power saving in an existing system is difficult in particular.